Most important wireless communication systems, such as Universal Mobile Telecommunication System (UMTS) or Long Term Evolution (LTE), have adopted asynchronous modes of operation, which means that there is no need of time-alignment between transmissions in different cells. However, there are some procedures, e.g. soft-handover in UMTS or some positioning algorithms in LTE, which require accurate timing information, so the 3rd Generation Partnership Project (3GPP) has standardized the report of time delay measurements.
Operators take advantage of this type of measurements to perform planning and optimization tasks based on positioned RF data, so a high degree of reliability is essential for accurate results. Nevertheless, any wireless communication suffers from multipath propagation, which includes the reception of two or more replicas of the transmit signal due to reflections in the atmosphere, terrain, buildings, etc. These reflections make the signal propagate longer than expected according to the line of sight, which may distort the reported time delay measurements. This effect is especially relevant in dense urban scenarios.
Multipath is intrinsic to wireless propagation and it especially affects positioning algorithms. A method for identifying and filtering multipath in Global Positioning Systems, GPS, based on signal-to-noise measurements is known from P. Strode, P. Groves, “GNSS multipath detection using three-frequency signal-to-noise measurements”, UCL Department of Civil, Environment and Geomatic Engineering. In the field of mobile communications, all cellular network measurements such as a Tm parameter defined in 3GPP TS 25.215 or a propagation delay (PD) are used in positioning algorithms, but are also very sensitive to multipath propagation. The Tm parameter defined in 3GPP TS 25.215 represents the subframe offset between a Primary Common Control Physical Channel (P-CCPCH) of a cell in a cellular network being measured and its existing Dedicated Physical Channel (DPCH) connection. The user equipment (UE) reports Tm measurements to acquire the required synchronization for soft-handover when certain events are triggered, e.g. a cell becomes better than a threshold. This information is included in the Radio Resource Control (RRC) measurement reports which are collected at an operation support system (OSS) and can be used by way of example in positioning methods based on the Observed Time Difference of Arrival (OTDOA).
However, a need exists to further improve the detection of multipath propagation.